Method of manufacturing a torque sensor

ABSTRACT

A torque sensor comprising a magnetic member whose magnetostrictive characteristics vary with the amount of torque applied thereto and coils for detecting magnetostrictive variation disposed opposite the magnetic member, and a method of manufacturing the same. The torque sensor is constituted as an independent unit separate from the shaft whose torque is to be measured. The independent unit consists of a cylindrical member having the magnetic member attached thereto and an enclosure member which is provided with the coils and is mounted so as to cover the cylindrical member and be rotatable about the same axis as the cylindrical member. The method of manufacturing the torque member comprises the steps of first copper plating and then solder plating a torque transmission member and a magnetic member destined to be attached to the outer circumference of the torque transmission member, wrapping the magnetic member on the torque transmission member, and solder-bonding the torque transmission member and the magnetic member by heating them while uniform pressure is being applied to the entirety of the wrapped region.

This is a divisional of co-pending application Ser. No. 019,599 filed onFeb. 26, 1987, now U.S. Pat. No. 4,817,444.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a torque sensor for detecting the torque of arotating shaft, more particularly to a magnetostriction type torquesensor for measuring the torque of a drive shaft, steering shaft orother rotating shaft of an automobile and the like, and to a method ofmanufacturing the same.

2. Description of the Prior Art

The indirect type torque sensor which measures the torque of a shaft bysensing the amount of twist therein is unable to measure static torque.Because of this inadequacy, there have recently been introduced a numberof direct type torque sensors operating on the principle ofmagnetostriction. As an example of such a torque sensor there can bementioned the one described in Japanese laid-open Patent Publication No.57(1982)-211030, wherein a ribbon-like magnetostrictive strip is woundon a shaft whose torque is to be measured. A similar torque sensor wasalso disclosed in Japanese laid-open Patent Publication No.59(1984)-166828.

The structure of the torque sensor disclosed by this publicationrequires that the magnetostrictive member (magnetic member) be fixeddirectly on the shaft whose torque is to be measured so that the shaftitself becomes one component of the torque sensor. This isdisadvantageous for several reasons. First, during manufacture of thetorque sensor, it is generally necessary to attach the magnetostrictivemember to a shaft of considerable length such as an automobile driveshaft, and this is difficult to do with high positional precision. Then,after the magnetostrictive member has been fixed on the shaft and up tothe time that the shaft is installed in the vehicle, which is generallylate in the assembly process, it is necessary to take great care intransporting and storing the shaft bearing the magnetostrictive memberso as to protect the member from damage and adherence of dust or thelike. The need to take these precautions greatly complicates the overallprocess of shaft installation.

Moreover, since the shaft whose torque is to be measured is involved asone component of the sensor, the sensor cannot be completed withoutmounting the other components on the shaft. As a result, it is notpossible to adjust the gap between the magnetostrictive member and theassociated coils until the assembly is carried out. Another disadvantagearises from the fact that drive shafts and other such automotive partsare only required to have adequate strength and are not required to havehigh dimensional precision. It therefore becomes necessary to use aspecial, separate adjustment means for adjusting the gap, which leads tofurther inconveniences as regards inventory control, performancecontrol, maintenance and the like.

Also, since the structure is such that the coil and other componentswhich are relatively susceptible to damage by mechanical shock are notcapable of being easily removed form the exterior, special care has tobe exercised during assembly and installation. This structure is alsodisadvantageous from the point of maintenance.

The conventional magnetostrictive type torque sensor has furtherrequired that a magnetic material exhibiting magnetostriction (e.g. amagnetic amorphous film) be attached to the outer periphery of thetorque transmission member or shaft. In this case, if a large gap ispresent between the torque transmission member and the magnetic memberattached thereto, an error is apt to arise in the measurement because ofslippage between these two members, while also disadvantageously cracksand other forms of physical degradation are likely to occur withprolonged use, thus shortening the service life of the sensor. It hastherefore been necessary to make every effort to minimize the size ofthe gap between the torque transmission member and the magnetic memberat the time of attachment. Methods aimed at achieving this are disclosedin Japanese laid-open Patent Publication 57(1982)-2110930 and elsewhereand include a method of mold-bonding the entire magnetic member using asynthetic resin bonding agent, a method of attachment by heat fusioninvolving spot welding or the like, a mechanical attachment methodinvolving the use of bands or the like, and a method involving copperplating followed by solder attachment. The first-mentioned method ofresin bonding has problems regarding heat resistance as well asdurability over prolonged use. The heat fusion (welding) method is notappropriate for use with a magnetic amorphous member since thecharacteristics of amorphous materials are easily degraded by heat. Asregards the third-mentioned mechanical attachment method, this is notcapable of providing reliable attachment over the entire attachmentsurface. While the last-mentioned solder attachment method has the bestpotential, it is still inadequate as regards durability.

SUMMARY OF THE INVENTION

In view of the aforesaid shortcomings of the conventional torquesensors, it is an object of the present invention to provide a torquesensor which is constituted as an independent unit separate from theshaft whose torque is to be measured and in which the shaft is notinvolved as a component of the torque sensor.

Another object of the invention is to provide a method of manufacturinga torque sensor wherein a magnetic member is securely attached to atorque transmission member or shaft with the gap between the two membersheld to the absolute minimum, degradation of the magnetic member by heatduring the attachment operation is prevented, and high durability overprolonged use is ensured.

For realizing these objects the present invention provides a torquesensor comprising a magnetic member whose magnetostrictivecharacteristics vary with the amount of torque applied thereto and coilsfor detecting magnetostrictive variation disposed opposite the magneticmember, the torque sensor being constituted as an independent unitseparate from the shaft whose torque is to be measured. The independentunit consists of a cylindrical member which can be freely mounted on andremoved from the shaft whose torque is to be measured and has themagnetic member attached to the surface thereof, and an enclosure memberwhich encloses the cylindrical member and has the coils attachedthereto.

The present invention further attains the aforesaid objects by providinga method of manufacturing a torque sensor comprising the steps ofseparately copper plating a torque transmission member and a magneticmember for attachment around the periphery thereof, solder plating thecopper plated members, wrapping the magnetic member onto the torquetransmission member, and solder-bonding the two members together byapplying heat over the entire wrapped portion while simultaneouslyapplying uniform pressure thereto.

The above and other features of the present invention will becomeapparent from the following description made with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the torque sensoraccording to the present invention;

FIG. 2 is a sectional view of the same taken along line II--II in FIG.1;

FIG. 3 is a sectional view of the same taken along line III--III in FIG.2;

FIG. 4 is an explanatory view for showing how coils are attached to theinner surface of a cover;

FIG. 5 is an explanatory view showing the method of attaching the torquesensor to a shaft whose torque is to be measured;

FIG. 6 is an explanatory view showing slits formed in a cylindricalmember and in a tapered ring;

FIG. 7 is an explanatory view showing the positioning of coils;

FIG. 8 is a block diagram illustrating the detection operation of thetorque sensor according to the invention;

FIGS. 9(a), 9(b), and 9(c) are explanatory views showing the steps forfabrication of a magnetic amorphous film;

FIGS. 10(a) and 10(b) show a magnetic amorphous film according to asecond embodiment of the torque sensor according to this invention;

FIG. 11 is a graph showing the results of a test in which the secondembodiment was compared with a conventional torque sensor;

FIG. 12 shows a magnetic amorphous film according to anothermodification;

FIGS. 13(a), 13(b), and 13(c) are explanatory views of a thirdembodiment of the torque sensor according to the invention;

FIGS. 14(a), 14(b), 14(c), 14(d), and 14(e) are explanatory views of afourth embodiment of the torque sensor according to the invention;

FIGS. 15(a), 15(b), 15(c), 15(d), 15(e), and 15(f) are explanatory viewsof a fifth embodiment of the torque sensor according to the invention;and

FIGS. 16(a), 16(b), 16(c), 16(d), 16(e), 16(f), 16(g), and 16(h) areexplanatory views illustrating the method of manufacturing the torquesensor according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To begin with, a first embodiment of the invention will be describedwith reference to FIGS. 1 to 9. As shown, a torque sensor 10 has acylindrical member 12. In the illustrated embodiment, the cylindricalmember 12 is substantially a true cylinder of circular cross-section andhas a bore 16 of a diameter slightly larger than the diameter of a shaft14 whose torque is to be measured. The bore 16 runs the full length ofthe cylindrical member 12. The arrangement is such that the shaft 14 canbe inserted into the bore 16, whereafter the cylindrical member 12 canbe fixed to the shaft 14 in a way that will be explained later. Thecylindrical member 12 has collars 18, 18 provided as annularprotuberances near either end, and the part of the cylindrical member 12between each collar 18 and the closer of the free ends is formed as atapered portion 20, 20. The part of the cylindrical member 12 betweenthe collars 18, 18 constitutes a cylindrical portion 22 of constantdiameter throughout its full length. The cylindrical portion 22 has amagnetic amorphous film 24 fixed thereon as by plating or some othermeans.

Fastening rings 26, 26 of an inner diameter larger than the outerdiameter of the cylindrical member 12 are fitted over the cylindricalmember 12 from opposite ends thereof. Each fastening ring 26 has ashoulder 28 which comes into abutting engagement with the associatedcollar 18, thus fixing the ring on the cylindrical member and preventingthe movement of the rings toward each other. The inner surface of thering 26 is formed with a tapered surface 30 extending outward from theshoulder 28 to near the outward end of the ring 26. The tapered surface30 is inclined oppositely from the tapered portion 20 of the cylindricalmember 12 so that a V-shaped recess is formed between the two. Theportion of the inner surface of the ring 26 extending outward from theouter end of the tapered surface 30 is formed with an internal thread32. A tapered ring 34 of wedge-shaped cross-section is inserted into theV-shaped recess and an externally threaded retainer ring 36 is screwedinto the threaded portion 32 of the ring 26 from the outside so as toabut onto the tapered ring 34. As a result, as the retainer ring 36proceeds inwardly, the tapered ring 34 is pressed progressively inwardso that the resulting wedge action causes the tapered portion 20 to bepressed onto the shaft 14. The cylindrical member is accordingly fixedon the shaft whose torque is to be measured. In the drawings, thereference numeral 38 denotes tool insertion holes formed in the retainerrings 36 for allowing insertion of the tool used for screwing in theretainer rings.

On the outer periphery of each of the fastening ring 26 is embeddedlyfitted a bearing 40, and immediately outward from each of the bearings40 there is disposed an oil seal 42. The reference numeral 44 indicatesa ring inserted to prevent lateral movement of the bearing 40.

Outward of the bearings 40 is provided an enclosure member 46 whichserves as an outer covering for the unit. As the enclosure member 46 iscoupled with the fastening rings 26 and the cylindrical member 12 viathe bearings 40, it is able to rotate independently of the fasteningrings 26 and the cylindrical member 12 so that when the cylindricalmember 12 rotates (together with the shaft 14), the enclosure member 46can be maintained stationary, i.e. can be prevented from rotatingtogether with the cylindrical member and the shaft. The referencenumerals 48 and 50 denote rings embeddedly fitted in the enclosuremember 46 for preventing lateral movement of the bearings etc.

As best shown in FIG. 3, the enclosure member 46 has a cylindrical innersurface and has one portion cut away to provide an opening. The openingis closed by a cover 52 which is fixed on the enclosure member 46 byscrews 54, 54 screwed into threaded holes provided in both the enclosuremember 46 and the cover itself through washers 56. In this connection,it should be noted that the cover 52 can alternatively be attached inany of various other ways, the only requirement being that the mode ofattachment allow removal of the cover 52 to the outside in the mannerthat will be explained later. A core 58 made of silicon steel sheetmaterial and having a yoke-like configuration when viewed fromunderneath (see FIG. 4) is attached to the cover 52 by stays 60 incombination with screws 62, washers 64 and nuts 66. As shown in FIG. 3,the steel core 58 is bowed so that the back surface thereof in contactwith the inside surface of the cover 52 has the same radius of curvatureas the inner surface of the cover 52. As a result, the core 58 can bemounted in close contact with the inside surface of the cover 52, which,as will be explained later, helps make it possible to ensure thatintercomponent gaps will be maintained uniform. A magnetic pole 68 isdisposed vertically near the center of the yoke-shaped core 58 and acoil is wound thereon to form an excitation coil 70. Further, twomagnetic poles 72, 72 are similarly disposed at symmetrical positionswith respect to the yoke-shaped core 58 so that one is positioned in thevicinity of the tip of each branch thereof. The magnetic poles are woundin opposite winding directions with coils so as to form a pair ofdetection coils 74, 74. The reference numerals 76, 78 and 80 denoteterminals of the respective coils. Thus, the coils and all othercomponents that are susceptible to damage by mechanical shock aremounted on the cover 52. As a result, in attaching the torque sensor tothe shaft whose torque is to be measured, it is possible to first attachthe main unit of the torque sensor to the shaft and then, after theattachment is completed, to attach the cover to the main unit from theoutside. This method of mounting the torque sensor results in improvedoperational efficiency and also makes it easier to replace coils andcarry out other maintenance work.

Next, the method of attachment of the torque sensor to the shaft whosetorque is to be measured will be explained, followed by an explanationof the method of use.

As shown in FIG. 5, for fixing the torque sensor 10 to the shaft 14, theretainer ring 36 and the tapered ring 34 are fitted over the end of theshaft 14 in this order and the end of the shaft 14 is then inserted intothe bore 16. Next, the tapered ring 34 is slid along the shaft 14 andinserted into the V-shaped recess between the tapered portion 20 and thetapered surface 30, whereafter the retainer ring 36 is slid along theshaft 14 and then screwed into the threaded portion 32. As shown in thefigure, this operation can be conveniently carried out using a tool 82having pins 84, 84 which fit into the tool insertion holes 38 of theretainer ring 36. As the retainer ring 36 is screwed in, it presses ontothe tapered ring 34 forcing it deeper into the recess and producing awedge effect on the tapered portion 20 of the cylindrical member 12. Asa result, the tapered portion 20 is pressed onto the shaft 14 and fixedso strongly thereto that no slippage can occur between the cylindricalmember 12 and shaft 14. In this connection, the fastening effect can befurther enhanced by providing both the tapered portion 20 and thetapered ring 34 with slits 86, 86 as shown in FIG. 6 so as to facilitatedeformation in the radial direction.

When the attachment has been completed in this way, any amount of torqueapplied to the shaft 14 will be transferred to the cylindrical member 12as a torque of identical magnitude. Thus, as is well known, thecompressive and tensile stress produced in the magnetic amorphous film24 as a result of this torque will give rise to magnetostrictiontherein. As a result of having been subjected to heat treatment and thelike in the presence of a magnetic field, the magnetic amorphous film 24is, as shown in FIG. 7, conferred with uniaxial magnetic anisotropy 88oriented at angles of ±45 degrees relative to the axis of thecylindrical member 12 and manifested mainly as compressive and tensilestress. Further, the aforesaid coils are arranged such that linesconnecting the magnetic poles thereof form a right isosceles triangle,with the pole 68 of the excitation coil 70 positioned at the uppermostright angle and the two poles 72, 72 of the two detection coils 74located at the respective lower 45-degree angles, and further with thepole 68 of the excitation coil 70 located at the branching point of theaforesaid uniaxial magnetic anisotropy. As a result, the flux paths 90between the excitation coil pole 68 and the respective detection coilpoles 72 coincide with the directions of the anisotropy, so that thepermeability is supplemented to the maximum.

In the torque sensor of the aforesaid structure, when, as shown in FIG.8, the excitation coil 70 is excited by application thereto of currentfrom an AC power source 92, the detection coils 74, 74 are able todetect any change in permeability resulting from magnetostriction causedby the aforesaid application of torque, and produce outputscorresponding to the electromotive force induced therein. Then whenthese outputs are differentially extracted, appropriately amplified byan amplifier 94 and rectified by a rectifier 96, it becomes possible todetermine the rotational direction from the phase of the outputs and todetermine the magnitude of the torque from the value of the outputs. Asthe detection outputs are extracted by use of differential connection,the shaft 14 will have no effect on the results of the measurement evenif it is made from a ferromagnetic material.

As shown in FIG. 9 (a), 9(b), and 9(c) an arrow-shaped or rectangularstrip is cut in a single punching action from a wide sheet of magneticamorphous film using a cutter 97 (FIG. 9(a)), thus fabricating themagnetic amorphous film 24 (FIG. 9(b)) which is then attached to thecylindrical portion 22 of the cylindrical member 12 by a plating methodor the like (FIG. 9(c)). As the cylindrical portion 22 has the collars18, 18 at its opposite ends, these can be used as positioning guides inthe attachment of the magnetic amorphous film 24. Thus, if the magneticamorphous film is cut precisely to the predetermined width and itsattachment is carried out using the collars as positioning guides, itbecomes possible to position the attached magnetic amorphous film atprecisely the predetermined position, which not only enhances theoperational efficiency of the fabrication work but also enables improvedmeasurement accuracy because it ensures that the distance between themagnetic amorphous film and the detection coils will be uniform alongall torque sensors manufactured in this way.

Since the torque sensor according to this invention is realized as anindependent unit which does not use the shaft whose torque is to bemeasured as one of its constituent elements, it need only to be attachedas it is to the shaft at some appropriate stage of the vehicle assemblyoperation. The cylindrical member to which the magnetic amorphous filmis attached is considerably shorter than a drive shaft or the like andis therefore much easier to handle. It also leads to improvedoperational efficiency from the point that its heat capacity is small.Further, the fact that the magnetic amorphous film is covered andprotected by the enclosure member results in an additional increase inoperational efficiency since less care is necessary for protecting itfrom damage and the adherence of dust and the like during transport,storage and mounting. While the fact that the torque sensor isconstructed as an independent unit might be expected to give rise toproblems if its attachment to the shaft whose torque is to be detectedshould be such that slippage could occur between the two, since undersuch circumstances it would not be possible to carry out accuratedetection, the torque sensor according to the present invention isentirely free from any such problem since it provides a highly reliablemethod of attachment based on the wedge effect of tapered rings.Moreover, since the number of components requiring precise positioningwith respect to one another has been kept to the minimum, it is notparticularly difficult in the course of fabrication to assure that thepositions of the bearings 40 and the dimensions of the enclosure member46, the cover 52 and the core 58 etc. are maintained within theprescribed tolerances. This, plus the effect obtained as a result of thecylindrical member and the enclosure member being cylindrical, enablesthe gap "d" (FIG. 3) between the coils and the surface of the attachedmagnetic amorphous film to be maintained at a constant magnitude, thuseliminating the need for any special adjustment means, making itpossible to realize a compact, light and low cost torque sensor, andreducing dimensional variance and, consequently, detection outputvariance among different torque sensors manufactured in accordance withthis invention.

Other embodiments of the torque sensor according to the presentinvention will now be described.

FIGS. 10(a) and 10(b) shows a magnetic amorphous film used in a secondembodiment of the torque sensor according to the invention. As will benoted from the developed view of the magnetic amorphous film shown inFIG. 10(a), the film is provided with a plurality of slits 98 sooriented that when the magnetic amorphous film is attached to thecylindrical member 12 as shown in FIG. 10(b), the slits 98 will make thesame angles of ±45 degrees with respect to the axis of the cylindricalmember 12 as the lines of uniaxial magnetic anisotropy 88, i.e. will liein the directions in which the variation in permeability is greatest. Asa result, the provision of the inclined slits produces an anisotropiceffect that derives from the configuration and as this anisotropy isadded to the uniaxial magnetic anisotropy 88, the variation inpermeability becomes even larger, meaning that the measurement accuracyincreases accordingly. It is also noteworthy that since the areaoccupied by the magnetic amorphous film is greater than that occupied byconventional rectangular shaped films, there is obtained a higher degreeof output sensitivity, and that even with the slits, the overallarrow-like configuration of prescribed width is still maintained so thatthe same improvement in operational efficiency is obtained as a resultof the attachment positioning enabled by the collars 18, 18 serving aspositioning guides on the cylindrical member. The graph of FIG. 11 showsthe result of a test in which the torque sensor according to the secondembodiment was compared with the beforementioned conventional torquesensor. In the test, the excitation frequency was 10 KHz, the excitationcurrent 50 mA, and both the excitation coil and the detection coils wereformed with 900 turns of coil wire, while the material of the shaftwhose torque was to be measured was made from SUS 304 steel.

Curve A shows the results obtained with the torque sensor according tothe present invention. Curve B shows the results obtained with theconventional torque sensor having four pairs of rectangular amorphousstrips attached directly on the measured shaft at 14 mm intervals.

At an applied torque of 80 kg-m, while the torque sensor in accordancewith the second embodiment of the present invention produced an outputof 900 mV as indicated by curve A, the conventional torque sensorproduced an output of only 230 mV.

FIG. 12 shows a modified version of the magnetic amorphous film shown inFIG. 10 wherein, for the purpose of obtaining enhanced matching with thedetection coils, the slits 98 are staggered and are extended to the edgeof the magnetic amorphous film. Aside from this modification, thearrangement is the same as that of the second embodiment.

A third embodiment of the torque sensor according to the presentinvention is shown in FIGS. 13(a), 13(b) and (c). Here the end portionsof the cylindrical member 12 are not tapered but are formed in aconstant diameter, and attachment to the shaft 14 is achieved using awedge-shaped tapered ring 100 that is flat on one side. This arrangementfacilitates fabrication of the cylinder portion and reduces the totalnumber of components required. In this embodiment, it is possible tofurther enhance the fastening effect by providing the tapered ring 100with slits 102 as shown in FIG. 13(c).

FIGS. 14(a)-(e) shows a fourth embodiment of the torque sensor accordingto this invention, wherein members corresponding to the cylindricalmember and fastening rings of the embodiment of FIG. 1 are integrated asa single cylindrical member 104. Similarly to the first embodiment,positioning collars 108, 108 are provided at either end of a cylindricalportion 106 for attachment of the magnetic amorphous film 24, while theportions outward from the collars 108, 108 up to the opposite ends ofthe cylindrical member 104 are not tapered but formed at a constantdiameter. A bearing 40 and an oil seal 42 are fitted on each of theseend portions and an enclosure member 46 is rotatably supported thereon.The outer edges of the end portions of the cylindrical member 104 areformed with a recess having an internal thread 110 near its outer end,followed by a tapered portion 112 which progressively narrows inwardlyuntil reaching an inner wall. The cylindrical member 104 is fixed to theshaft 14 whose torque is to be measured by the frictional force obtainedbetween these two members when a first tapered ring 114 formed with twowedge-like surfaces and a second tapered member 116 formed with a singlewedge-like surface (FIG. 14(b)) are forced onto the tapered portion byscrewing a threaded retainer ring 118 into the threaded portion of therecess. In place of the rings 114 and 116, there can be used a ring 120(FIG. 149c)) corresponding to what would be obtained by integrating thesaid two rings 114, 116. It is also possible to further enhance thegripping force provided by the rings 114 and 116 by providing them withslits 122 as shown in FIG. 14(d). Further, it is convenient to providethe ring 114 (or 120) with threaded holes 126 as shown in FIG. 14(e) sothat when the ring is to be removed the operation can be facilitated byscrewing screws 128 into the holes 126 until they strike against theinner wall of the cylindrical member 104, whereafter further turning ofthe screws 128 will result in a reaction force tending to urge the ring114 (120) outward and away from the tapered portion. Thus whilefeaturing the same ease of attachment to the shaft as the earlierdescribed embodiments, the torque sensor according to this fourthembodiment provided with the ring removal means can, if necessary, alsobe demounted from the shaft with utmost ease after once being mountedthereon. In its other aspects, this fourth embodiment is the same as thefirst embodiment. Reference numeral 130 in the figure denotes a cover.The ring 114 (120) in FIG. 14(e) may be divided into a plurality ofsegments.

The fifth embodiment of the torque sensor according to the inventionillustrated in FIGS. 15(a)-(e) involves a further modification of thecylindrical member whereby the length of the cylinder end portions 132extending outward from the collars are made shorter than in theembodiments described so far, and the retainer rings and associatedthreads are eliminated. A first tapered ring 134 and a second taperedring 136 are used here. Here the attachment is realized by the clampingaction obtained when the first tapered ring 134 is forced inward byscrewing a plurality of clamping screws 138 in thread holes formed inthe portion 132 through smooth holes 140 formed in the ring 134 (FIG.15(b)). Alternatively, it is possible to use an integrated ring 142 asshown in FIG. 15(c), to provide the ring 136 with slits as shown in FIG.15(d), to use a ring 134 (or 142) divided into a plurality of segmentsas shown in FIG. 15(e) or to use the ring 134 (or 142) further formedwith threaded holes 144 adapted for accommodation of ring removal screws146. The structure and effect of the removal means are substantiallyidentical to that of the fourth embodiment.

While in the embodiments described in the foregoing, a magneticamorphous material is used for the magnetic member, the invention is notlimited to this and may use any material exhibiting magnetostrictiveproperty.

The method of manufacturing the torque sensor according to the inventionwill now be explained with reference to FIGS. 16(a)-(h).

As shown in FIG. 16(a), the cylindrical portion 22 of the cylindricalmember according to the first embodiment of the invention is firstprovided with a copper plating 150 and then on top of this with a solderplating 152. The purpose of providing the copper plating 150 is tofacilitate the adherence of the solder plating 152.

In parallel with the above, a magnetic amorphous film 24 is similarlyprovided with a copper plating 154 and over this with a solder plating156 (FIG. 16(b)).

Next, as shown in FIG. 16(c), the magnetic amorphous film 24 is woundonto the cylindrical member 12 with the solder plated surfaces facingeach other. The magnetic amorphous film 24 is formed in the generalshape of an arrow and its dimensions are so determined that when it iswrapped once about the cylindrical member 12, the point of the arrowwill fit into the notch thereof.

Then as shown in FIG. 16(d) and the sectional view along "e--e" line ofFIG. 16(e), a wide, heat-resistant rubber band 158 is placed over theportion of the cylindrical member wound with the magnetic amorphous film24. The width of the rubber band 158 is made the same as that of themagnetic amorphous film 24, i.e. equal to the wrapped portion (thedistance between the collars 18, 18), and, as a result, the wrappedportion receives a uniform pressure over its entire area.

Next, as shown in FIG. 16(f), the cylindrical member 12 with the rubberband 158 thereon is heated by leaving it to stand in a high-temperaturetank 160. The temperature within the high-temperature tank 160 iscontrolled by a temperature control unit 162 so as to maintain it withinthe range of 280°-300° C., a temperature range in which the magneticamorphous film 24 suffers no degradation. Heating in the tank isconducted for about 5 to 10 minutes. As the heating in the tank isconducted while the surfaces to be adhered are pressed onto each other,the fused solder moves into all gaps present between the cylindricalmember 12 and the amorphous film and that which finds no gaps to fill isforced out to the exterior.

The cylindrical member is then removed from the tank 160 and cooled, asshown in FIG. 16(g), whereafter the rubber band is removed. Thiscompletes the bonding operation.

The cylindrical member bearing the magnetic amorphous film is thencombined with the enclosure member shown in FIG. 1 and the succeedingfigures to obtain a fully assembled torque sensor.

In the manufacturing method according to the invention, since the solderis fused by leaving the cylindrical member in the high-temperature tankwith a uniform pressure being applied over the bonding area by therubber band, the fused solder permeates throughout the whole area ofcontact between the cylindrical member and the magnetic amorphous filmso that no unbonded regions remain. Also since the solder is fused underuniform pressure applied over the entire area by the rubber band, asshown in FIG. 16(h) the distance "w" representing the bonding thicknessbetween the inner surface of the magnetic amorphous film 24 and theouter surface of the cylindrical member 12 is held to a very small valuewhich is uniform over the entire of area of attachment. As a result, nocause exits for slippage between the cylinder member 12 and the magneticamorphous film 24, or for the development of cracks in the magneticamorphous film 24. Further, the uniformity of this thickness also meansthat the distance between the outer surface of the magnetic amorphousfilm 24 and the coils referred to earlier is maintained constant,resulting in improved measurement accuracy by the torque sensor. Inaddition, the lack of any voids in the bonding results in an improvementin the service life.

The following test was carried out to observe the performance of thetorque sensor manufactured according to the invention. The torque sensorwas fabricated using the magnetic amorphous film measuring 4 cm in widthand the cylindrical member made of a non-magnetic material (SUS) andmeasuring 3 cm in diameter and 65 cm in length. Both of these membersare subjected to copper plating followed by solder plating. The magneticamorphous film was then wound on the cylindrical member and the rubberband was fitted thereover to apply a pressure of 2 kg/cm² to themagnetic amorphous film. The cylindrical member was then left to standin the high-temperature tank for 10 minutes. The temperature within thetank was maintained at 300° C. The cylindrical member was removed fromthe tank and allowed to cool for 30 minutes. It was then used tofabricate a torque sensor such as that shown in FIG. 2. The torquesensor was mounted on a shaft for measuring the torque thereof. In theinitial measurement, the torque sensor measured the torque within arange of error of ±10%. Twenty test cycles were then carried out forobservation of durability. The error in the final test cycle was ±10%,meaning that there was no degradation with use. No cracks or other flawswere observed in the bonded surface.

Since the torque sensor according to the invention is constituted as anindependent unit separate from the shaft whose torque is to be measured,in its fabrication it suffices to attach the magnetic member to acylindrical member which is much shorter than said shaft, so that thereis realized a major improvement in the operational efficiency of, forexample, an assembly process for an automobile equipped with the torquesensor. Also, there are realized advantages in regard to the control ofcomponent dimensional accuracy, particularly regarding maintaining auniform gap between the surface of the magnetic amorphous material andthe coils, which makes it possible to manufacture torque sensors withreduced variance in performance from unit to unit.

In addition, the manufacturing method according to the invention enablesthe torque transmission member and the magnetic member to be attached toeach other uniformly without any unbonded regions being left betweenthem and with the separation between these two members being held to avery small uniform value throughout their entire area. As a result,there is no risk of slippage occurring between the magnetic member andthe torque transmission member, so that there is obtained both animprovement in measurement accuracy and a longer service life.

The present invention has thus been shown and described with referenceto specific embodiments. However, it should be noted that the presentinvention is in no way limited to the details of the describedarrangements but changes and modifications may be made without departingfrom the scope of the appended claims.

What is claimed is:
 1. A method of manufacturing a torque sensorcomprising the steps of:a. plating a torque transmission member and amagnetic member destined to be attached to the surface thereof firstwith copper and then with solder, b. wrapping the magnetic member ontothe torque transmission member, and c. solder-bonding the torquetransmission member and the magnetic member by heating them whileuniform pressure is being applied to the entirety of the wrapped member.2. A method of manufacturing a torque sensor according to claim 1wherein the heating is carried out at a temperature of not more than300° C. for a period of 5 to 10 minutes.
 3. A method of manufacturing atorque sensor according to claim 2 wherein the torque transmissionmember is a separate member from the shaft whose torque is to bemeasured and is constituted as a cylindrical member mountable on saidshaft.
 4. A method of manufacturing a torque sensor according to claim 1wherein the torque transmission member is a separate member from theshaft whose torque is to be measured and is constituted as a cylindricalmember mountable on said shaft.
 5. A method of manufacturing a torquesensor including a torque transmission member having a magnetic metallicfilm, comprising the steps of:plating solder onto the torquetransmission member and magnetic film respectively forming solder platedsurfaces on said member and said film; wrapping the metallic film ontothe torque transmission member with the solder plated surfaces of thetorque transmission member and metallic film facing each other; andheating the torque transmission member and metallic film to be solderedwhile pressing the metallic film onto the torque transmission member. 6.The method of claim 5 further comprising the steps of plating the torquetransmission member and metallic film with copper prior to solderplating.
 7. The method of claim 6 wherein said heating is carried out ata temperature of not more than 300° C. for a period of approximatelyfive to ten minutes.
 8. The method of claim 7 wherein the metallic filmis pressed onto the torque transmission member at a pressure ofapproximately 2 kg/cm².
 9. The method of claim 5 wherein said torquetransmission member comprises a cylindrical member which is mountableonto a shaft whose torque is to be measured.
 10. The method of claim 9wherein said film comprises a magnetostrictive amorphous film having auniaxial magnetic anisotropy along a pre-determined angle with respectto a longitudinal axis of said torque transmission member.
 11. Themethod of claim 10 wherein said metallic film has a plurality of slitsformed along said uniaxial magnetic anisotropy.
 12. The method of claim11 wherein said slits are staggered with respect to each other.